Korean tennis player Chung Hyeon claimed the biggest win of his career as the 20-year-old won over world No. 16 Gael Monfils in the second round of the BMW Open men's tennis tournament in Munich, Thursday.

Chung, 78th in the world rankings, defeated Monfils 2-0 (6-2, 6-4) in 72 minutes to secure a quarterfinal berth.

The match was suspended at 6-2, 3-3 for about 90 minutes due to rain. With the defeat, the French veteran lost his chance to claim his 400th match win.

Chung expressed his overflowing joy. "I'm so happy as it's the biggest win of my career," he told ATPWorldTour.com.

"It was a tough match against Gael and I tried to stay calm all the time," he said. "The rain delay was tough, but it's the same for all the players. I tried to keep the rallies long, as this is his first tournament on clay. I will be ready for tomorrow and I will keep trying my best."

The French player, who had six ATP World Tour titles, also praised his opponent Chung after the match.

"He played a really solid match and he was better than me," Monfils said. "It's good to be back on the court, rather than practicing. It wasn't easy and I had a lot of mis-hits, but Hyeon pushed me a lot." The ATP added Monfils will now look to the Mutua Madrid Open to become the 17th active player with 400 wins, joining his fellow Frenchmen Richard Gasquet (468), Gilles Simon (412) and Jo-Wilfried Tsonga (405).

Chung's next match will be with Martin Klizan, the winner of the 2014 event. The 27-year-old Slovakian advanced to the quarterfinals after defeating Mischa Zverev of Germany 2-0 (6-2, 6-1).